Field of the Invention
The invention relates to a method for foaming or foam-coating components, in which a material inserted into cavities of double-walled or multiple-walled components or located between a surface of a component and a decorative material, is expanded in order to form a foam filling. The invention also relates to a foamable material for performing the method.
There is an increasing demand for components simultaneously having a high rigidity and a reduced weight. The cavities of multiple-walled components are normally filled with foam through the thermal decomposition of an expanding-agent system fixed in the foam-forming polymer material through compounding or through filling in with a foam which is under an over-pressure, which expands in the cavity, and which reacts with moisture from the air and thereby hardens.
Since expansion is already taking place during insertion into the cavities, it is easy for regions not filled with foam to be left in the space to be filled with foam, thereby leading to a considerable reduction in quality. Therefore, in the case of longitudinally extended cavities, cavities formed in complicated structures or large cross-sections, it is necessary to introduce the foam into the component at several places through a number of drillings. That is a method which is not only very complicated but still does not guarantee a uniform foaming.
It is also known to improve the visual effect of components through coating with decorative material such as films, leather or textiles and at the same time to achieve an improved tactile quality. That is done by providing a layer of foam which should possess variable thickness and consistency, between the surface of the component and the decorative material. However, the attachment of a foam backing of that kind which, as is known, proceeds in combination with a decorative material, is associated with difficulties since the foam collapses in strongly shaped regions or, in the case of more rigid foams with greater wall thicknesses, the composite of foam and decorative material cannot be attached crease-free to the component.
In a known method for the fabrication of molded parts with a foam-backed decorative coating having advantageous visual and tactile qualities, the decorative material is first coated at its rear surface with an unfoamed material and after the decorative material has been positioned, the as yet unfoamed or pre-foamed layer on the back surface is expanded through the intrinsic heat of the component to be coated and/or heat applied in addition. As a result of non-uniform conduction of heat or a temperature gradient at the respective component, it is not always possible to ensure a uniform thickness and softness of the layer of foam between the component and the decorative layer.